Lamps of the above type are traditionally halogen light source based and used in halogen spots. These traditional halogen light source based lamps are now to a rising extend being exchanged with LED based lamps of the above type used as retrofits for halogen lighting devices.
Therefore, the demand for an energy saving alternative to existing types of LED-based lamps is very high. Removing the considerable heat generated by the light source is a challenge, which normally necessitates limiting the power, and thus the light output, to levels below what is desired, the use of a heatsink having a size exceeding the outline of the lamp or the inclusion of a fan for active cooling.
Most LED based lamps share the same layout: a central cylindrical body surrounded by a metallic structure with fins working as a heatsink.
The cylindrical body, which usually has a diameter of less than 50 mm, contains the light sources, the optics and the driver assembly. Depending on the driver topology, LED type and number, and optics, the diameter of the cylindrical body may be very large, leaving very little space for the cooling fins.
U.S. Pat. No. 8,018,136 B2 describes an LED connector assembly comprising an LED, a driver assembly and a heat sink having a cylindrical core aperture. The driver assembly comprises a driver card mounted in guide slots extending on opposite sides of the core aperture and configured to receive the driver card. The driver card comprises slots mating with end walls of the guide slots. The electronical components of the driver assembly are arranged on the driver card such as to be positioned within the core aperture.
These known types of lamps have several disadvantages. First of all the thermal resistance (Rth) of the heatsinks is too high to fulfill the requirements for high power applications. The large circular cross section of the central aperture of the known solutions reduces the volume available for the heat dissipating fins of the heat sink resulting in an insufficient air flow. This has been targeted as the main reason for the insufficient thermal resistance of the known lamps. Moreover, the position of the driver assembly results in a rather long thermal path from the components to the heatsink, leading to an elevated average temperature of the driver assembly components being about 7° C. above the temperature of the outskirts of the heat sink.
Furthermore, the space available for the driver assembly is insufficient. The driver requirements in terms of volume and area for the printed circuit board (PCB) of the driver assembly are stringent and hard to achieve within the form factors of the known types of lamps.
Also, while the thermal rating, i.e. the temperature for which they are rated to be able to work without being negatively affected, of most of the components both of the driver assembly and related to the light source is above 125° C., some of them, such as electrolytic capacitor(s), are more sensitive to high temperatures. Therefore, the more thermally sensitive components need to be arranged such as to be better protected from high temperatures. However, the construction of the known types of lamps results in an unsuitable arrangement of both the driver assembly components and the light source components with respect to their thermal rating, as thermally sensitive and heat generating components are arranged closely together.